1. Field of Invention
The invention relates generally to blast surface treating machines whereby particulate material is thrown with centrifugal force from a rotating blast wheel onto a surface so that paint, dirt, burrs and the like are removed and, more particularly, to a blast surface treating machine wherein the particulate material is fed to the rotating blast wheel through an oscillating control cage via a screw conveyor and that features an anti-shattering construction.
2. Description of Prior Art
Blast surface treating machines of the type indicated generally at 20 in FIG. 1 are well known in the art. Such machines feature a hopper 22 within which a supply of particulate material 24 is maintained. The particulate material may be steel shot, sand, gravel or the like. A blast wheel 26 featuring throwing blades 28 is mounted to the hub of a motor 32 and rotates at a high velocity about an axis 33. The hopper communicates with the center of the blast wheel via feed spout 34 so that the particulate material is supplied to the center of the rotating blast wheel. As a result, the particulate material is propelled by centrifugal force through a passage defined by guard housing 36 towards a surface 42 such as steel or concrete from which paint, dirt or burrs are to be removed. After rebounding off of the surface, the particulate material, along with the debris removed from the surface, travels through the rebound chute 44 to the hopper. A fan (not shown) may be used to create an airflow through the rebound chute towards the hopper. The debris is removed from the hopper via a dust collection arrangement 46.
The details of a typical prior art blast surface treating machine are illustrated in FIGS. 2 and 3. Such machines are available from The Wheelabrator Corporation of La Grange, Ga. As described above, the machine features a blast wheel 50 equipped with throwing blades 52. The blast wheel is mounted to a hub 54 which is connected to a shaft 56 by bushing 58. The shaft is rotated by a motor such as the one indicated at 32 in FIG. 1.
A control cage 62 is positioned within the cylindrical space defined by the inner edges of the blades of the blast wheel. As shown in FIG. 4, the control cage is cylindrical and features an opening 64 as well a serrated edge 66. The control cage is secured to adapter plate 68 which is secured to guard housing 72. Guard housing 72 is secured to base plate 74 which has an opening 76. More specifically, the control cage is secured to the adapter plate via clamp 82 and bolt 84 so that the orientation of opening 64 may be adjusted. The control cage remains fixed as the blast wheel rotates.
An impeller 86 is also secured to shaft 56 via bolt 90 and is sized to rotate freely within the control cage. As a result, the impeller rotates along with the blast wheel. As shown in FIG. 5, the impeller is also cylindrical and features multiple openings 92. A feed spout 94 supplies particulate material to the impeller from a hopper such as the one indicated at 22 in FIG. 1. As the impeller spins, the particulate material is forced through the control cage opening 64 and onto the blast wheel blades 52. As a result, the particulate material is propelled by centrifugal force towards a surface through opening 76. The particulate material leaves the blasting wheel at an angle of approximately 180.degree. from the control cage opening 64.
While blast surface treating machines of the type described above perform admirably, they suffer from disadvantages. The width of the path treated as the machine is moved along a surface, called the blast pattern or "hot spot", is limited by the size of the control cage opening and the position of the machine relative to the surface. A larger control cage opening produces a wider blast pattern. If the opening is too large, however, the machine will bog down and the velocity of the particulate material will decrease. This will adversely impact the treating ability of the machine. A larger distance between the machine and the surface will also produce a wider blast pattern. If the distance is too great, however, the particulate material will lose velocity before it impacts the surface so that treating is adversely impacted. Furthermore, spacing the machine a great distance from the surface requires a more cumbersome guard housing and makes recovery of the particulate material difficult. The size of the control cage opening and the distance of the machine from the surface being treated therefore must be limited. As a result of these limitations, the blast pattern width of prior art blast surface treating machines is typically approximately six inches. A wider blast pattern would allow a surface to be treated with a fewer number of machine passes. In addition, a wider blast pattern would provide more uniform treating of a surface in that there would be less overlapping treated portions of the surface.
The impeller, control cage and blast wheel of prior art blast machines are typically constructed of cast metallic material. As a result, the components are very brittle. Objects such as screws, bolts or the like may accidently fall into the hopper of a blast surface treating machine. Such an object would travel to the impeller and be forced out of the control cage opening. As a result, the object could be wedged or pinched between the rotating impeller and the fixed control cage opening. When this occurs with prior art machines, the impeller, due to its brittleness, shatters and the resulting debris is passed out onto the blast wheel blades. As a result, the blast wheel blades may also shatter.
Accordingly, it is an object of the present invention to provide a blast surface treating machine that provides a wider blast pattern.
It is another object of the present invention to provide a blast surface treating machine that features an anti-shattering construction.